The present invention relates to devices for providing an electrical interface between a patient and an electrical physiological monitoring, sensing or measuring equipment. More particularly, the present invention relates to apparatus capable of effecting a temporary electrical interconnection between the skin surface of a patient and the input connection for electrical medical data acquisition equipment and is particularly useful in establishing a secure but adaptably flexible electrical interface between a selected area of the skin and the input for electrical physiological measuring, sensing or detecting systems such as electrocardiograms and other electrical monitoring systems of the type which require a low, constant resistance interconnection with a patient.
A variety of devices have been developed in the past for acquiring medical data on a patient from electrical parameters associated with the patient. Some devices sense the electrical conductivity within the patient while others measure various other parameters including internal resistance and the like. Such medical electrical measurement or testing systems are necessarily sensitive because of the low levels of electrical activity involved and require relatively constant and low resistance interfacing with the skin of the patient. It was early recognized that merely strapping an electrical connector to the skin of a patient would produce an unpredictable interface resistance thus discounting the measurement acquired. An early practice has been to specially treat the skin area of the patient so as to reduce the electrical resistance at the surface and to include a conductive gel between the electrode and the skin of the patient to further reduce the interface resistance. Thus a variety of devices have been developed for the purpose of combining the adhering functions and the conductive gel retaining functions in a common housing. For instance, Phipps et al No. 3,170,459 shows an electrode combination formed of a plurality of bonded insulator layers with an electrode connector button exposed to a cavity in which gel can be inserted. Similar unitary electrode connector assemblies have been shown in Mason U.S. Pat. No. 3,518,984, Yuan U.S. Pat. No. 3,572,323 and Weyer U.S. Pat. No. 3,845,757. An electrode with a snap-on connector and an oversized conductive gel retaining disc for filling the cavity under the connector in response to attachment compression is shown in U.S. Pat. No. 3,882,853 by Gofman et al.
However, the aforementioned prior art connectors are difficult to recharge or clean and sterilize for reuse particularly where an internal cavity is incorporated. Ultrasonic cleaning of the gel cavity type electrode is reasonably satisfactory but necessarily delays availability of the electrodes for further use. One approach that has been suggested for avoiding delays in electrode availability is to use disposable electrodes such as in Sessions U.S. Pat. No. 3,805,769 wherein a bonded disc arrangement with a snap-type of connector is formed as a unit and thrown away after utilization. However, it is important that the connector button for the electrode exhibit high quality electrical interfacing characteristics, silver and silver chloride combinations being particularly attractive in this regard. Thus the use of such materials for the electrode is prohibitively expensive for inclusion in a disposable application. Furthermore, although many of the prior art interfacing electrode assemblies are reasonably satisfactory for static measurement, it is frequently important that the electrical measurements be continuously maintained even during relatively violent physical activity in order to acquire meaningful data on the patient. Security of the interface connection under such conditions is vital since a loose connection will result in noisy readings and useless data. Beyond this, there is a need for an electrical interfacing apparatus which can remain attached to a bed-ridden patient for continuous monitoring of vital functions and the like.
Therefore, there has been a continuing need for an electrical interfacing arrangement between a patient and medical sensing or monitoring apparatus which establishes a reliably secure attachment while accommodating movement of the patient without detracting from the constant, minimal resistance at the interface. Furthermore, there is a continuous need for an interfacing arrangement which permits retention of the more expensive electrode so that it can be quickly and effectively prepared for further use while allowing disposal of the less expensive conductive gel.